Megalopygidae (flannel moths)
Adult flannel moths are chunky-bodied, and the bodies, legs, and wings are very hairy, giving them a fluffy appearance. Most are whitish, yellowish, or brownish, with few markings. The females have thin antennae and males have featherlike antennae; often, the two sexes have slightly different colorations, too.
Caution! The fuzzy, hairy, silky caterpillars in this moth family can sting. They do not actively attack people, but if you brush against these caterpillars, stinging hairs, hidden among nonstinging hairs, can poke into your skin and break off, and venom inside the hairs or spines can penetrate your skin (this is a lot like the spines of stinging nettle plants). Reactions vary depending on the type of caterpillar and a person’s individual sensitivity. Stinging, itching, burning, rash, lesions, dermatitis, swelling, even fever and even nausea can result.
Caterpillars of flannel moths differ from those of all other butterflies and moths by their number of prolegs. Prolegs are the fleshy, peglike legs along the abdominal segments (that is, behind the pointy, jointed thoracic legs at the front of the caterpillar). Flannel moth caterpillars have 7 pairs of prolegs, while all other butterfly and moth caterpillars have 5 or fewer pairs.
Caterpillars in many moth families have stinging or irritating hairs, but then again, not all hairy caterpillar species necessarily can irritate or sting. If you are uncertain about the identification of any hairy or spiny caterpillar, dead or alive, it’s best not to touch it.
Most US flannel moths are limited to the desert southwest or the extreme southeast (especially Florida). Apparently three species are likely to be found in Missouri:
Wingspan: 1–1½ inches.
Flannel moths fly statewide in forests from spring until late summer or early fall. As with other moths, flannel moths occur most commonly near their food plants. Because the caterpillars of these moths tend to have a wide variety of suitable food species, they might be found in many places. They are usually only locally common, and they generally occur in small numbers.
Caterpillars feed on leaves of suitable species of trees and shrubs. The mouthparts of adults are reduced, and apparently they do not eat at all.
Statewide. They seem to be most numerous in the southern and eastern parts of our state.
Like other moths, flannel moths begin life as an egg, then hatch into small caterpillars that feed and grow, molting a number of times before forming a pupa and emerging as a winged, sexually mature adult. Fully-grown caterpillars overwinter in a strong cocoon molded to the trunk or branches of the host plant before pupating in the spring. Females cover their eggs with abdominal hairs.
If you are “stung” by one of these caterpillars, wash the area to remove any stinging hairs or toxin that remain on your skin. You can also try applying tape to the area, sticky side down, then removing it to pull the hairs out of the skin; repeat with fresh pieces of tape until the spines are gone. Using an ice pack can reduce swelling, and steroidal lotions or creams (such as hydrocortisone) can help with discomfort and swelling. Applying a paste of baking soda and water can be helpful. If you know that you are sensitive to insect stings, or if the pain or swelling is intense, worsens, is badly blistered, or doesn’t go away within 1 to 12 hours, consult a doctor.
It seems like a cruel hoax — that something so invitingly soft and fuzzy can zap us with irritating stings. But it’s a reminder that the natural world does not always follow our preferences, and it functions according to a logic we don’t always see.
The stinging hairs on flannel moth caterpillars function, of course, for defense. A bird, mammal, or other predator attempting to eat one of these hairy creatures will be powerfully dissuaded by immediate stinging and burning. This allows the caterpillar to continue feeding in peace.
The hairs probably also serve to help the caterpillar regulate its body temperature and hydration levels, since they must help insulate, shade, and buffer the effects of strong wind on the tender body within.
Butterflies, skippers, and moths belong to an insect order called the Lepidoptera — the "scale-winged" insects. These living jewels have tiny, overlapping scales that cover their wings like shingles. The scales, whether muted or colorful, seem dusty if they rub off on your fingers. Many butterflies and moths are associated with particular types of food plants, which their caterpillars must eat in order to survive.